Descriptive epidemiology of the burden of human monkeypox in Nigeria: a retrospective review 2017-2021

Abstract

INTRODUCTION: Sporadic outbreak of human monkeypox (hMPX) has been reported in 20 non-endemic countries as of the first quarter of 2022. One of these cases was epidemiologically linked to an individual with a history of previous visits to Nigeria. The purpose of this study was to determine the burden of hMPX in Nigeria, determine its hotspots and epidemic threshold from 2017-2021. METHODS: we reviewed reports on the outbreak of hMPX disease from the Nigerian centre for disease control (NCDC) between 2017-2021. We identified States affected, determined the number of confirmed monkeypox cases, and conducted a Geospatial analysis with Arc Geographical information system (ArcGIS), to describe the Hotspots of hMPX outbreaks in Nigeria classified as (major/high, medium, minor/low) clusters based on disease burden in affected states. We calculated the epidemic threshold (EPT) of outbreaks based on cumulative sum, (CUSUM) statistics, (C1-C3) for October 2017-2021. The epidemic threshold was based on the formula; EPT equals (=) Mean(α) + 3 standard deviations(δ) of seven past surveillance points of the year under consideration skipping over the two surveillance points before the month under consideration. RESULT: in 2017, 88 confirmed cases of hMPX were reported in Nigeria in 15 States, River State accounts for 25(28%) of cases, Bayelsa State 19(22%) was identified as major hotspots for hMPX, 13 States reported minor clusters of 44 cases, individuals aged 21-30 years 34(39%), were at higher risk. In 2018, 49 confirmed cases of hMPX were reported in Nigeria in 13 States, River State accounts for 14(29%) of cases, Bayelsa State 11(21%) were major hotspots for hMPX, 11 States reported minor clusters of 24 cases, individuals aged 31-40 years 17(35%) were at higher risk. In 2019, 47 confirmed cases of hMPX were reported in Nigeria in 11 States, Lagos State accounts for 15(32%) of cases, Delta State, 10(21%) were major hotspots for hMPX, Rivers and Bayelsa State accounts for 7(15%) and 7(15%) of cases were medium clusters of hMPX, 7 other States reported minor clusters of 8 cases, individual aged 31-40 years 22(47%) were most affected. In 2020, 8 confirmed cases of hMPX were reported in Nigeria in 5 States Lagos State with 4(50%) of cases, was a major hotspot for hMPX, four other States accounted for minor clusters of four cases, individual aged 21-30 and 31-40years 4(50%), 4(50%) respectively were most affected. In 2020, 34 confirmed cases of hMPX were reported in Nigeria in 9 States, Delta State accounts for 9(27%) of cases, Lagos State, 6(18%), and Bayelsa 6(18%) were the major hotspots. Rivers and Edo State with 5(15%) and 4(12%) of cases were medium clusters, four other states had minor clusters of four cases, individuals aged 31-40 years, 13(38%) were at high risk. The epidemic threshold for hMPX was (12, 8, 1, and 4) respectively. CONCLUSION: monkeypox is endemic in Nigeria, 226 confirmed Human Monkeypox (hMPX) cases were reported with 8 fatalities across 20 States. Young adults aged 21-30 years are at a higher risk of infection. The disease is clustered in two geopolitical zones (South-west/South-south) of Nigeria. The observed hMPX cases were higher than the epidemic threshold in 2020 and 2021 such may have contributed to the sustained sporadic outbreak of monkeypox reported as of the first quarter of 2022, the risk factors included consumption of giant rats/monkeys, occupational hazard amongst health care workers, individual who frequent crowded social gathering. Consequently, improved screening for hMPX at the border post, and enhanced in-country surveillance may ensure early detection, and prevent the spread of hMPX. Furthermore, training of health care workers on increased risk perception of hMPX may reduce occupational hazards. These measures should be complemented with public enlightenment of high-risk populations.